Sleep Calculator
A sleep calculator determines the best bedtime or wake-up time based on 90-minute sleep cycles. Waking in the middle of a deep sleep stage causes grogginess (sleep inertia), while waking between cycles feels natural and refreshing.
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Tip: Even a 20-minute "power nap" between 1–3 PM can restore alertness without disrupting nighttime sleep. Longer naps (>30 min) risk sleep inertia and disrupted night sleep.
- 1An average sleep cycle lasts 90 minutes (NREM stages 1–3 + REM)
- 2Most adults need 5–6 complete cycles (7.5–9 hours)
- 3It takes approximately 14 minutes to fall asleep after lying down
- 4To find bedtime: subtract (cycles × 90 min + 14 min) from wake-up time
- 5To find wake-up: add (cycles × 90 min + 14 min) to bedtime
Wake up at 7:00 AM=Bedtimes: 9:46 PM (6 cycles), 11:16 PM (5 cycles), 12:46 AM (4 cycles)6 cycles = 9 hours of sleep
Sleep at 11:30 PM=Wake times: 5:14 AM (4 cycles), 6:44 AM (5 cycles), 8:14 AM (6 cycles)
| Stage | Type | Duration | Function |
|---|---|---|---|
| N1 | Light NREM | 5–10 min | Transition to sleep |
| N2 | Light NREM | 20 min | Heart rate slows, temperature drops |
| N3 | Deep NREM | 20–40 min | Physical restoration, immune function |
| REM | REM sleep | 10–60 min | Memory consolidation, dreaming |
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Fun Fact
REM sleep lengthens in later cycles — your first REM stage is about 10 minutes; the last (before waking) can be 60 minutes. This is why you often remember dreams from the morning.
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